20-Year Prospect
There's one thing that will never get old. Staring into the eyes of your nemesis, who is longing to bring you in for your laundry list of crimes, and sneering "diplomatic immunity" at him. That's probably why foreign service officers have a 90% retention rate (source).
We're not suggesting you go out and start a criminal empire here. Merely pointing out that this kind of job, diplomat, okay, okay, foreign service officer seems like a pretty great gig once you get it. Those who get the job hold on for dear life, so it's something you could be doing for two decades and beyond. Additionally, it's not like you suddenly become terrible at it. A long life in the job gives you experience and contacts that are invaluable for your performance.
You want job security? This is it. It's not like all of a sudden other countries are going to stop existing. People just don't like John Lennon quite that much. The U.S. has more than 270 diplomatic posts throughout the world (source) and that number isn't likely to get smaller anytime soon.